A torque limiting coupling of this type is described in Italian patent application No. FI/95/A/56 filed Mar. 23, 1995 by the same applicant, and in the corresponding European Patent Application n. 96830108.5, U.S. Pat. application Ser. No. 08/620,006 and Canadian Pat. Appl. N. 2,172,120.
These transmission couplings generally have two or more possible angular positions in which coupling can occur, a corresponding number of components for effecting the coupling being arranged in an angular distribution. This sometimes raises a problem for these transmission couplings, for which it would be desirable for coupling to occur in a unique angular position.
The abovementioned intellectual property document discloses in particular a transmission coupling that comprises: on the internal surface of the outer member, recesses with lead-in surfaces running parallel to the axis of rotation; inside the inner member, essentially radial seats allowing movement and defined by two planar walls parallel to the axis of rotation of the coupling, said essentially radial seats for allowing movement being equal in number to said recesses with lead-in surfaces; in each of said essentially radial seats for allowing movement, a sliding key resembling a tablet in shape and able to move radially under the action of elastic means in a centrifugal direction, and with a shaped outer profile able to enter one or other of said recesses with lead-in surfaces of the outer member, in order to transmit torque between said two members and generate centripetal radial forces on the sliding key.